The pipeline method batches multiple operations into a single IPC call. A smaller chunk_size value is needed to notice the difference.

      # increment shared hash - single IPC per chunk
      $count->pipeline(
         map { [ 'incrby', $_ => $lcount{$_} ] } keys %lcount
      );
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Comparison chunk_size => 1_000

Before 0.814 seconds  $count->incrby(...)
 After 0.522 seconds  $count->pipeline(...)
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Regards, Mario